Various electrolyzers have been employed in chlor-alkali industry. In a diaphragm process, a deposition. diaphragm electrolyzer is commonly used. In this electrolyzer, power-supply rods are mounted vertically and its diaphragm is attached on a cathode screen by means of deposition, which has disadvantage that the diaphragm has lower strength, poor surface flatness, and uneven distribution of mass construction and results in lower content of alkali and higher content of chloride in a cathode electrolyte.
A membrane process develops fast since 1980s and has a tend to replace the prior diaphragm process with the advantages that this membrane process has a lower energy-consuming and that the product manufactured thereby can meet not only general requirement but also special requirement such as in the artificial fiber industry. However, high price and vulnerability of an ion-exchange membrane used in the membrane process result in a high requirement of the machining precision of the electrolyzer used therein.
Generally, a mono-polar pre-filter electrolyzer is one that used in the membrane process, in which horizontal or inclined power-supply rods are provided or no rods are provided. The electrolyzer has disadvantages of high manufacturing cost and can not be obtained by reforming the prior deposition diaphragm electrolyzer. Therefore, the replacement of the deposition diaphragm electrolyzer with this electrolyzer shall be finished in one time after whole system stops operating when a chlor-alkali manufacturer converts from the diaphragm process to the membrane process, which means that such replacement can not go on progressively as the system is operating.
The conventional mono-polar pre-filter electrolyzer with power-supply rods also has the disadvantages that the number of its horizontal or inclined power-supply rods has to be increased when a much higher electrolyzer is desired, which results in higher resistance to an up and down circulation of fluid in the electrolyzer, and that it requires larger floor area to site considering the difficulty of the increase of its height. A prior technology to convert the deposition diaphragm electrolyzer to the electrolyzer used in the membrane process is to reform the deposition diaphragm electrolyzer to a tank type membrane electrolyzer, but both working and assembly of the tank type membrane electrolyzer can not reach higher precision. In addition, this tank type electrolyzer consumes more membranes up to 40-150% and its current density is lower to 20-60% in operation than the conventional mono-polar pre-filter electrolyzer.
British patent No. UK 8103008 discloses an electrolyzer without power-supply rods used in the membrane process. Because the electrolyzer has no power-supply rods, its interior current route can not be longer than 25 cm, resulting in a restricted dimension of the anode. In order that the dimension of the anode is not restricted any more, Chinese patent No. 91101030.0 (publishing date: Sep. 25th, 1991) discloses an electrolyzer which has horizontal power-supply rods connecting with a bus to transmit electric current into the electrolyzer. Chinese patent No. 9010777.1 (publishing date: Mar. 13rd, 1991) discloses another electrolyzer which has horizontal and inclined power-supply rods. However, the power-supply rods arranged in this manner cause a higher resistance to the circulation of gases produced in electrolysis reaction. Therefore, the electrolyzer has to be added with some accessories to form passageway which is used for fluid circulation, which results in difficulty in increasing the height of the electrolyzer. Moreover, The above electrolyzers used in the membrane process are not able to obtain by reforming the prior deposition diaphragm electrolyzers when the diaphragm process is converted to the membrane process. In addition, the chlor-alkali manufacturer can not replace the electrolyzers during the system is operating.
An electrolyzer used in the membrane process and obtained from the deposition diaphragm electrolyzer is disclosed in Chinese Patent CN 86105810 A (publishing date: Feb. 18th, 1987), and its improvement is described in &lt;&lt;China Chlor-alkali&gt;&gt; No. 5, 1993. However the electrolyzer disclosed therein is a mono-polar tank type rather than the mono-polar pre-filter type. Because the tank type still has a box constitution similar to that of the deposition diaphragm electrolyzer, the membrane needs adhering to be in a bag shape. As a result, the membrane consumes more and the operating current density is 2000-2500 A/M.sup.2 which is lower, and the electrolyzer is worse than that of the mono-polar pre-filter type on the record of operation and economy indicator.
It is an object of the present invention to overcome the disadvantages of prior art and provides a mono-polar pre-filter electrolyzer with vertical power-supply rods. When the electrolyzer is applied in the membrane process, its all records of operation, technology and economy are similar to those of the conventional mono-polar pre-filter electrolyzer. Moreover, the increase of its height is not restricted and it can be obtained by reforming the prior deposition diaphragm electrolyzer.
It is a further object of the present invention to provide an electrolyzer which can replace from the deposition diaphragm electrolyzer one by one as the system is under operation, when the deposition diaphragm process is converted into the membrane process.